As is elaborated below, Topoisomerase I (Top1) and Phosphodiesterase I (Tdp1) are involved in DNA replication, transcription and repair; and it appears that inhibition of either enzyme, or both of them, is useful in treatment of disease, particularly in cancer. Certain N-substituted indenoisoquinoline compounds have been reported which inhibit the activity of Top1 and have potential in cancer chemotherapy. See for example US-2008-0318995-A1.
It has been discovered that N-substituted indenoisoquinoline compounds are useful as inhibitors of Tdp1 and that some of them inhibit both Tdp1 and Top1. Further, novel N-substituted indenoisoquinoline compounds which inhibit Top1 and/or show anticancer activity have been discovered.